The present invention relates generally to a mixing impeller device and method. More particularly, the present invention relates to an impeller for mixing and blending materials such as gases, liquids and liquid suspensions.
Mixing and blending applications, in particular the mixing and blending of liquids, liquid suspensions and gases, are often constrained by the diameter of the tank in which the mixing is being carried out and by the diameter of the impeller. Some high solidity impeller designs (or xe2x80x9cgas foilsxe2x80x9d) compensate for the aforementioned constraints by using impellers with three or four blades each having a large projected area. For example, it is known for existing high solidity impeller blades to occupy 80% of their total swept area. In addition, some existing impeller designs use impeller diameters which are typically 45% to 65% of the tank diameter. For a vessel of 240xe2x80x3 (20 feet) in diameter, the impeller diameter is approximately 120xe2x80x3 (10 feet) in diameter depending on service requirements, and the blades are approximately 60xe2x80x3 long and at least 38xe2x80x3 wide.
The impeller blades need to be inserted through a manway in the vessel for installation. In some covered mixing vessels, manways are commonly 24xe2x80x3 in size and can pass impeller blades of up to 23xe2x80x3 in width at best. Therefore, in order to insert larger blades, users either have to install an oversized manway, (40xe2x80x3 in size for a 240xe2x80x3 diameter tank), or the blades must be supplied in a longitudinally split configuration and then assembled inside the vessel. Splitting the impeller blades is an expensive operation, especially for blades having a rounded, leading edge, twist and curvature. In addition, multiple bolts are required along with match marking to assure proper, gap free re-assembly. This process can be very difficult and time consuming because the inner and outer blade components must be aligned correctly so that the impeller balance and blade geometry will not be compromised.
Further, some blades of known impeller design utilize a xe2x80x9cblade to earxe2x80x9d bolted connection for providing torque transmission, thrust reaction and blade support, in which the blades are each attached to an ear extending from the shaft. The blades use symmetrical bolt patterns of 4, 5, 7 or more bolts to attach the blade to the ear of the hub. This connection must be carefully designed, manufactured and assembled to assure problem free installation of the blades.
Also, known impeller designs usually provide 3 to 4 blades per impeller. Thus, 12 to 28 bolts are required for blade attachment, and alloy bolts are often required. Alloy bolts are expensive and, depending on the material, of limited availability. Many users require the use of positive locking of impeller bolts and hardware through the use of locking plates, double nuts and/or safety wire, increasing the total cost of each bolt. Due to the large quantity of bolts, it is usually not practical for the end user to retighten the impeller hardware after the initial period of operation, which can cause a loss of pre-load and premature failure of the bolted connection.
Accordingly, it is desirable to provide a high solidity impeller for mixing gas and liquid materials that offers improved reliability, reduced cost and ease of installation.
The present invention relates to impellers and impeller systems for mixing and blending applications. The invention is especially suitable for use in applications where the vessels are closed and are relatively large in diameter.
In one aspect, the invention provides an impeller assembly that is mountable onto a rotatable shaft that has a flange extending radially from the shaft and rotating with the shaft. At least one blade pair member has two opposed blades and a central hub portion having a hole therethrough with an inner diameter at least as large as the outer diameter of the shaft. A plurality of corresponding mounting holes is provided in each of the flange and the blade pairs, and a plurality of bolts for fastening the blade pair to the flange via the mounting hole is provided.
In another aspect of the invention, the impeller assembly further comprises at least one additional blade pair. The blade pairs are stacked onto one another, so that the blades extend radially at angular intervals to each other. The mounting holes align so that the bolts fasten all of the blade pairs to the flange.
In a third aspect of the invention, the flange has a frictional fit key member and is releasably frictionally fit at a location along the length of the shaft.
In yet another aspect, the invention provides a method for mounting an impeller assembly onto a rotatable shaft having a flange radially extending from the shaft. The method comprises the steps of inserting at least one member that has two opposed blades and a central hub portion that has a hole therethrough with an inner diameter at least as large the outer diameter of the shaft onto the shaft and into contact with the flange. The method provides for fastening the blade pair member to the flange so that it rotates with the shaft.
In a further aspect of the invention, the method additionally comprises the step of fastening a second blade pair member having two opposed blades and a central hub portion having a hole therethrough with an inner diameter at least as large as the outer diameter of the shaft onto the shaft in a stacked fashion onto the at least one blade pair member.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract included below, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.